The tetrahydrocannabinoids, (-)-delta-8-THC-DMH, (-)-delta-9-THC, and (-)-delta-8-THC, specifically reduce the turnover rate of acetylcholine in the hippocampus and the turnover rate of GABA in septum in a dose-dependent manner. The (plus) isomer of delta-8-THC fails to alter these parameters. These results suggest that the tetrahydrocannabinols are activating specific receptor binding sites probably in the septum. However, this high degree of nonspecific binding of 3H-delta-8-THC due to its high lipid solubility precludes the use of a rapid filtration method with glass fiber filters to document the presence of specific recognition sites for these compounds.